1. Field of the Invention
The present invention relates to a laser diode.
2. Description of the Related Art
A buried heterostructure (BH) has been known as one of the structures of laser diodes used in fiber-optic communications. A BH laser diode includes a stripe-shaped semiconductor mesa portion and burying layers which are arranged on both sides of the semiconductor mesa portion. The semiconductor mesa portion includes an active layer. The BH laser diode can strongly confine light and current in a portion near the active layer. The BH laser diode thus has excellent properties, i.e., a low threshold current, high slope efficiency, and high output power. The burying layers may be composed of a semi-insulating semiconductor. The BH laser diode including the burying layers composed of the semi-insulating semiconductor has a low parasitic capacitance and excellent high-frequency characteristics. For this reason, the BH laser diode is suitably used as a light source for use in fiber-optic communications.
Japanese Unexamined Patent Application Publication No. 02-206192 discloses such a BH laser diode. The BH laser diode disclosed in this patent document includes a semi-insulating semiconductor layer and an n-type semiconductor layer formed on the semi-insulating semiconductor layer as semiconductor burying layers. The semi-insulating semiconductor layer is composed of, for example, Fe-doped InP. The n-type semiconductor layer is composed of, for example, n-type InP. A p-type semiconductor layer (p-type cladding layer) is formed on a semiconductor mesa and the n-type semiconductor layer of the semiconductor burying layers.